Apparatus for reducing flowing fluid pressure with low noise generation

ABSTRACT

Fluid pressure reducing apparatus presenting low noise throttling plates. The low noise fluid pressure throttling apparatus provides an assembly of a plurality of such plates, and which may comprise a segment of or be interposed in a fluid flow containing conduit. The low noise throttling plates are passaged by multiple small section orifices producing a high frequency pressure wave whose noise is more readily attenuated by the conduit. The spacing of the plates in the pressure reducing assembly defines with the intervening flow containing means a volume which is dimensioned to produce resonant damping of the noise pressure wave generated in the primary orifices. The pressure drop through the reducing apparatus is divided into nearly equal ratio drops across each plate, further minimizing noise generation.

United States Patent Baumann [4 1 May 30, 1972 541 APPARATUS FORREDUCING 1,229,434 6/1917 FLockhart .Q ..181/69 FLOWING FLUID PRESSUREWITH Low NOISE GENERATION FOREIGN PATENTS OR APPLICATIONS [72] Inventor:Hans D- Bauma'nn Foxbom' Mass 117,203 7/1918 Great Bntam ..181/69 [73]Assignee: Masoneilan International, Inc., Norwood, PrimaryExaminer-Samuel B. Rothberg Mass. Anamey-Chittick, Pfund, Birch, Samuels& Gauthier 22 F '1 2 7 red May 6,19 0 ABSTRACT 21 A l. N .2 40 607 1 pp0 fluid pressure reducing apparatus presenting low noise throttlingplates. The low noise fluid pressure throttling apparatus [52] 1.1.5. Cl..138/42, 181/46, 251/127, provides an assembly of a plurality of suchplates, and which 181/56 may comprise a segment of or be interposed in afluid flow [51] It. CI ..FlSd 1/00 containing c ndui[ The low noisethrottling plates are [58] Field of Search ..138/42; 181/46, 69, 33.9,36.2, pasaged by multiple small section rifices producing a h 181/56?251/127; 285/49 frequency pressure wave whose noise is more readilyattenuated by the conduit. The spacing of the plates in the pressure[56] References Cited reducing assembly defines with the interveningflow contain- UNITED STATES PATENTS ing means a volume which isdimensioned to produce resonant damping of the noise pressure wavegenerated 1n the pnmary 1,697,481 1/1929 Sloan.. ..181/69 rifices, Thpressure dro through the reducing apparatus is 2,677,23 1 5/1954Corneliusx divided into nearly equal ratio drops across each plate,further 2,075,3 Tyden 1 8 noise generation. 2,520,089 8/1950 Lippincott138/40 1,914,072 6/1933 Boylston ..181/69 12 China, 3 Drawing FiguresPatented May 30, 1972 3,655,965

2 Sheets-Sheet 1 O IQ INVENTOR HANS D. BAUMANN BY ird, 9 r

ATTORNEYS FIG. 2

Patented May 30, 1972 3,665,965

2 Sheets-Sheet 2 INVENTOR HANS o. BAUMANN cum 1:10:19 SM ATTORNEYSAPPARATUS FOR REDUCING FLOWING FLUID PRESSURE WITII LOW NOISE GENERATIONBACKGROUND OF THE INVENTION The invention pertains to apparatus forreducing the pressure of gaseous or liquid media flowing through a pipeor duct, and more particularly for accomplishing the fluid pressurereduction with minimum or greatly reduced generation of noise, orunwanted sound. The problems attendant upon the annular of noise arewell known to include not only the human reaction criteria of annoyance,damage to hearing, and reduction in work efi'lciency, but also theeffects on physical structures and equipment, such as structuralfatigue, and equipment malfunction.

In industrial plants, gas pressure reducing stations, and the like whereare found the throttling valve or aerodynamically generated soundeffects with which the invention is particularly concerned, the noiseproblems attendant thereon are rapidly intensifying in absolute terms,and have attained more recently a magnitude heightened also be increasedhuman sensibility to noise pollution. But noise control efforts haveheretofore been limited generally in this country to the use'ofmufflers, attenuation chambers and the like, or devices for absorptionor insulation of the generated noise. This invention, in contrast, cutsthrottling noise at the source, and thereby achieves superior resultsboth in reducing throttling noise and in reducing mechanical vibrationfrom levels experienced with conventional pressure reducing valves.

BRIEF SUMMARY OF THE INVENTION In view of its novel aspects, thetheoretical considerations on which the invention is rested are here setforth in aid of its full and clear understanding by those skilled in theart.

Fluid dynamic theory predicates a high dependence of the hereinconcerned throttling noise energy on the pressure drop ratio and fluidflow velocity. High pressure differentials across a jet or constrictionin the fluid flow generate noise energy which increases at a rategreater than the rate of increase in the pressure drop in ratio. Thenoise or vibration energy generated also varies with the eighth power ofthe fluid velocity in the jet. Both a high velocity, and a pressure dropratio, then, lead to high accoustical efficiency, or high energyconversion to noise.

By far the most efficient way to reduce throttling noise is, of course,todecrease the velocity of the flow. In accomplishing this by increasingthe effective flow area only some of the resultant noise reduction isoffset by the noise being a function also of flow area.

Any solid or fluid medium vibrating in response to noise energy waveswill convert a portion of the energy it receives to heat. With fluids itis the fluid viscosity which occasions the conversion, or damping. Asimilar noise energy damping reaction occurs as well in solids.

Further, the amount of energy passed on through such media varies withthe negative power of the distance that the energy travels within themedium. And in solids like the metals found in pipes, the attenuation inthe medium increases with the frequency of the noise energy.

It is thus an object of the present invention to provide apparatus forpressure reduction or throttling of fluid flow with a low accousticalefficiency.

It is a further object of the invention to provide an accoustical filterfor absorbing downstream the noise of conventional valves and therebypreventing the radiation of that noise through the fluid conduit wallsto its external surroundings.

It is a further object of the invention to provide a device forthrottling fluid flow with greatly reduced noise generation by minimumfluid velocity constricting jet means.

It is a further object of this invention to provide a pressure reducingor throttling device having constricting jet means characterized bylowered pressure drop thereacross.

It is a further object of the present invention to provide a pressurereducing apparatus which increases the viscous damping of the noiseenergy in the flowing fluid.

It is a further object of the present invention to provide a fluidpressure throttling device which generates noise at a frequency whichprovides for greater attenuation of the noise energy by the fluidconduit.

It is a further object of the invention to absorb part of theaerydynarnically created noise by a process of resonant damping withinsaid throttling device.

BRIEF DESCRIPTION OF DRAWINGS In the drawings:

FIG. 1 is a plan view of the invention apparatus; and

FIG. 2 is a section along any bisecting'line of FIG. 1; and

FIG. 3 is a perspective view of a modified form of the apparatus.

DETAILED DESCRIPTION OF THE INVENTION In the fonn of FIGS. 1 and 2 ofthe drawings a herein circular, radially symmetrical conduit C is shownas having an inner wall defining two axially in-line parts 3a, 3b whichextend to either side of a ring or annular spacer 4. The spacer 4 has alarger diameter, cylindrical'inner face 5 coaxial with conduit axisA--A', and an intermediate, annular, infacing flange or lip 6 of fullcircumferential extent.

A pair of transverse wall forming means or plates 7, 9 having a tightfit within spacer 4 are held by suitable means, herein the collars 8 and11, against the opposite faces of lip 6. The collars 8 and 11 are inturn closed against the plates 7, 9 by the ends of smaller diametershoulders of conduit parts 3a, 3b when the same are assembled with thespacer 4 as by external clamping means which may be conventional andare, therefore, not shown.

Under the invention, the plates 7, 9 may be parallel mounted with thering 4 in a rigid assembly or frame in any desired manner, and whereinthe circumferentially containing means 4 is inserted in or is a portionof the conduit C.

Upstream plate 7 is passaged by a multiplicity of jet orifices or holes12. The number of holes 12 is great, and their crosssectional area issmall. The holes 12 will be understood to be utilized in a number:cross-sectional area combination which for a given fluid at a given ormaximum expected flow rate produces the desired low pressure drop acrossthe plate 7, in

the fluid flow traversing, the same in the left-right direction A-A.

Under the invention the holes 12 are made numerous and individually ofsmall cross-sectional area also to increase the vibratory frequency ofthe noise energy accompanying the pressure drop in said flowing fluid.

Most of the noise energy generated in the upstream set of holes 12 isradiated by pressure waves from a region of noise energy turbulencedownstream of plate 7, and tends to proceed out through the walls of theconduit C. In responding to these pressure waves, the conduit C absorbsa portion of the energy from the waves by damping effect of the conduitmaterial.

This attenuation by the conduit may be expressed as:

A 17 log (mf) where m mass density of the wall and f frequency of thevibration.

The frequency is, of course, a direct function of the passages or holediameter. Under the invention, then, by reducing the diameter of theupstream holes 12, and thereby increasing the frequency of the noiseenergy generated therein, a larger portion of the noise energy isattenuated in the conduit walls, and a corresponding reduction isachieved in the noise radiated to or polluting the environment.

The downstream plate 9 has a set of orifices or holes 14 which are seenas offset from the holes 12. The number and cross-sectional area ofthese holes is again adjusted to the desired pressure drop, for a givenfluid and flow rate, and is selected also and novelly to provide, asbefore, increased frequency of vibration of, and thereby enhancedconduit wall attenuation of, the generated noise.

By varying the size and number of the holes 14 in the downstream plate9, compensation is made for the change in fluid density by the reductionin pressure through the upstream plate 7. Further, the totalcross-sectional area of the holes 14 is made larger than the totalcross-sectional area of the holes 12, by the provision either of more orlarger holes 14 through the second plate 9.

In accordance with the invention, then, the pressure drop across theperforated plates 7 and 9 is split up into equal or substantially equalratios. This results in a substantial decrease of the overall noiselevel, since as above noted, the level of noise energy generated in ajet increases more rapidly than the rate of increase in the pressuredrop ratio across the jet. In other words, by thus keeping the pressuredrop ratio across each perforated plate smaller, there is achieved areduction of noise energy generated, over that for a single plate with ahigher accoustical efficiency in noise generation due to its higherpressure drop.

For example, with a total pressure drop ratio of 4 the accousticalefficiency for a single plate is 36 times greater than the efficiency itwould have with a pressure drop ratio of 2 across its set of holes. Withtwo plates each producing a pressure drop ratio of 2 the total noiseenergy from the two plates in one-eighteenth what it would have beenwith a single plate.

Centrally, a fastening or bolt 16 having a head 17 is passed through anoversized opening in one of the plates 7, 9 and through an interveningcollar 18 and threaded into the other of the plates 7, 9, in part tointermediately clamp the plates 7, 9 together with the spacer 6 in aunitary assembly, or frame.

The bolt 16 may also mount various flow restricting means such as theflow regulating plate 19, which may be positioned between the plates 7and 9, or upstream of plate 7, the same to effectively block a portionof the first and/or second of the channel sets 12, 14 thereby reducingthe flow capacity of the plates so as to maintain the same totalpressure drop under different, reduced flow conditions.

The aforementioned offsetting of the downstream holes 14, as clearlyshown in FIG. 2, will be understood to improve the pressure reducingcapability of the plates 7, 9 and at the same time to enhance theresonant effect in the cavity or volume 21 defined by or within theframe formed by the plates 7, 9 and the spacer 4. The longitudinal oraxial length of the collar 18 and the spacer lip 6 then, is calculatedto comprehend or contain the desired amount of fluid within the framevolume 21. For a particular conduit, and given that the resonantfrequency of the volume 21 varies with its size, the same can becontrolled, then, by adjusting the length as aforesaid of the collar 6and spacer 18.

The equation relating the plates 7, 9 may be stated as:

f Ac/2 Vk where A total area of the holes contained in the first plate7;

c the speed of sound in the fluid used;

V= the volume of the cavity 21; and

k a constant.

By making a resonant frequency of the volume 21 nearly equal to thefrequency of noise energy generated in the holes 12 of the upstreamplate 7, large resonant pressure differentials will be built up in thevolume 21 at that frequency. Through the process of resonant damping,and due to the viscosity of the fluid, the high resonant pressuredifferentials result in an increased conversion of noise energy to fluidheat.

It will be understood that the pressure reducing apparatus of theinvention may comprise the plates 7, 9 and also any other transversewall forming means susceptible of channeling by jet passages such as thehole sets 12, 14.

Further, the desired resonant cavity may under the'invention be providedby a volume 21 having shape and proportion other than that defined bythe frame spacer 6 and plates 7, 9 herein particularly disclosed anddescribed.

Still further, the resonant cavity may be defined by and within a framecomprising a plurality other or more than the described two spacedtransverse plates, or other wall forming means.

Thus, in FIG. 3 is shown a modified embodiment comprising a plurality ofthree transverse plates, incorporating upstream plate 7 and a pair ofdownstream plates 9, 22. In this arrangement, the downstream plate 22will be understood to have openings 23 having the similar position andproportion relationship to the openings 14 of downstream plate 9 as thelatter have to the openings 12 of upstream plate 7. Also, the plates 7,9, 22 will be understood to define resonant cavities, and to divide theframe volume, in accordance with the invention teachings as hereinbeforeexplained.

To accommodate the additional plate 22, the modified ring 4a may have alip 6a against which upstream plate 7 is held by collar 8, anddownstream plate 9 is engaged by insert ring 24, against the oppositeface of which the downstream plate 22 is in turn held by collar 11. Andmodified bolt 16a will be understood to be passed through intermediateplate 9 for threading into downstream plate 22, with the plates beingspaced thereat by a pair of the collars 18.

Also shown in FIG. 3 is one expedient for closing the ends of conduitportions 3a, 3b against the sides of the rings 4a, comprising integralflanges 25, 26 on said conduit portions 3a, 3b, and a series of radiallydisposed nut and bolt or similar fastenings 27 therethrough as shown.

It will also be understood that the frame hereof may comprise thedescribed plate pluralities and the intervening conduit wall portion asdefined by the herein disclosed spacer, or by the securing of the wallforming means or plates to the conduit inner wall and in spaced assemblyin any other desired or convenient manner.

Further, in accordance with the invention, the plate assembly or framehereof may be utilized in downstream conjunction with a conventional,single orifice throttling valve. It will be appreciated that in suchapplication the low noise plates hereof operate to filter the majornoise emanating from the throttling valve, preventing the noise fromtravelling into the downstream pipe and hence from radiating throughthat to the outside environment.

I claim:

1. Low noise generating apparatus for reducing the pressure of fluidflow in a conduit, comprising:

a. upstream transverse wall means;

b. multiple, small, flow throttling passages of calculated the numberand/or size of said multiple, small, flow throttling passages relativelyincreasing, and said calculated total areas of said passagesprogressively increasing in constant ratio, from each to the next in thesuccession of said upstream and downstream transverse wall means,

said multiple, small, flow throttling passages in said upstream anddownstream transverse wall means provided in such determined largenumber and small cross section as radiates noise energy at a frequencyat which it is highly attenuated within said conduit, and whereby itaccords the apparatus low accoustical efficiency; and

e. means circumferentially containing the fluid flow intermediate saidupstream and downstream throttling passages and forming with saidtransverse wall means a frame supporting and spacing said throttlingpassages,

said circumferentially containing means comprising, with the one or morepairs of any two adjacent of said upstream and downstream transversewall means, one or more resonant damping chambers,

each said resonant damping chamber defining, by the spacing of saidtransverse wall means, a volume calculated to produce the resonantfrequency of the sound waves generated by the fluid flow through saidtransverse wall means.

2. The apparatus of claim 1, wherein the number and/or size of thethrottling passages of one is varied from the number and/or size of thethrottling passages of other adjacent of said upstream and downstreamtransverse wall means such as to divide the pressure drop across saidapparatus into substantially equal ratio pressure drops across theindividual of said upstream and downstream transverse wall means.

3. The apparatus of claim 1, wherein the throttling passages of one areoffset in the flow direction from the passages of another of saidupstream and downstream transverse wall means.

4. The apparatus of claim 1, wherein said transverse wall means areplates, and wherein said throttling passages are holes defining jetorifices in said plates.

5. The apparatus of claim 1, wherein said transverse wall means compriseannular plates, and wherein said circumferential containing meanscomprises a spacer ring.

6. The apparatus of claim 1 and means uniting said transverse wall meanscentrally of said circumferential containing means, said centrallyuniting means comprising a fastener engaging and adapted to drawtogether said transverse wall means.

7. The apparatus of claim 6, and spacer means limiting said drawingtogether by said fastener, said spacer means comprising one or morecollars, and said fastener engaged behind one of said transverse wallmeans, passed through said one or more collars, and adjustably securedto another said transverse wall means.

8. The apparatus of claim 1, and means positioning said transverse wallmeans for determined upstream-downstream spacing of said flow throttlingpassages.

9. The apparatus of claim 1, and means for adjusting the flow capacityof said frame.

10. The apparatus of claim 9, wherein said flow capacity adjusting meanscomprises means for closing a determined portion of the passages of oneor another of said wall means.

11. The apparatus of claim 10 wherein said passage closing meanscomprise plate means removably supported against the upstream side ofsaid one or another wall means.

12. The apparatus of claim 11, wherein said plate means are carried onfastener means removably securing together said wall means centrally ofsaid circumferential containing means.

1. Low noise generating apparatus for reducing the pressure of fluidflow in a conduit, comprising: a. upstream transverse wall means; b.multiple, small, flow throttling passages of calcUlated total area inand establishing small fluid pressure drop across and high frequency ofnoise generation by said upstream wall means; c. one or more downstreamtransverse wall means; d. multiple, small, flow throttling passages ofcalculated total area in and establishing small fluid pressure dropacross and high frequency of noise generation by said one or moredownstream wall means, the number and/or size of said multiple, small,flow throttling passages relatively increasing, and said calculatedtotal areas of said passages progressively increasing in constant ratio,from each to the next in the succession of said upstream and downstreamtransverse wall means, said multiple, small, flow throttling passages insaid upstream and downstream transverse wall means provided in suchdetermined large number and small cross section as radiates noise energyat a frequency at which it is highly attenuated within said conduit, andwhereby it accords the apparatus low accoustical efficiency; and e.means circumferentially containing the fluid flow intermediate saidupstream and downstream throttling passages and forming with saidtransverse wall means a frame supporting and spacing said throttlingpassages, said circumferentially containing means comprising, with theone or more pairs of any two adjacent of said upstream and downstreamtransverse wall means, one or more resonant damping chambers, each saidresonant damping chamber defining, by the spacing of said transversewall means, a volume calculated to produce the resonant frequency of thesound waves generated by the fluid flow through said transverse wallmeans.
 2. The apparatus of claim 1, wherein the number and/or size ofthe throttling passages of one is varied from the number and/or size ofthe throttling passages of other adjacent of said upstream anddownstream transverse wall means such as to divide the pressure dropacross said apparatus into substantially equal ratio pressure dropsacross the individual of said upstream and downstream transverse wallmeans.
 3. The apparatus of claim 1, wherein the throttling passages ofone are offset in the flow direction from the passages of another ofsaid upstream and downstream transverse wall means.
 4. The apparatus ofclaim 1, wherein said transverse wall means are plates, and wherein saidthrottling passages are holes defining jet orifices in said plates. 5.The apparatus of claim 1, wherein said transverse wall means compriseannular plates, and wherein said circumferential containing meanscomprises a spacer ring.
 6. The apparatus of claim 1 and means unitingsaid transverse wall means centrally of said circumferential containingmeans, said centrally uniting means comprising a fastener engaging andadapted to draw together said transverse wall means.
 7. The apparatus ofclaim 6, and spacer means limiting said drawing together by saidfastener, said spacer means comprising one or more collars, and saidfastener engaged behind one of said transverse wall means, passedthrough said one or more collars, and adjustably secured to another saidtransverse wall means.
 8. The apparatus of claim 1, and meanspositioning said transverse wall means for determinedupstream-downstream spacing of said flow throttling passages.
 9. Theapparatus of claim 1, and means for adjusting the flow capacity of saidframe.
 10. The apparatus of claim 9, wherein said flow capacityadjusting means comprises means for closing a determined portion of thepassages of one or another of said wall means.
 11. The apparatus ofclaim 10 wherein said passage closing means comprise plate meansremovably supported against the upstream side of said one or anotherwall means.
 12. The apparatus of claim 11, wherein said plate means arecarried on fastener means removably securing together said wall meanscentrally of said circumferential containing means.